1. Field of the Disclosure
Embodiments disclosed herein relate generally to downhole tools. In particular, embodiments disclosed herein relate to expandable underreamers and related methods of use.
2. Background Art
In the drilling of oil and gas wells, typically concentric casing strings are installed and cemented in the wellbore as drilling progresses to increasing depths. Each new casing string is supported within the previously installed casing string, thereby limiting the annular area available for the cementing operation. Further, as successively smaller diameter casing strings are suspended, the flow area for the production of oil and gas is reduced. Therefore, to increase the annular space for the cementing operation, and to increase the production flow area, it is often desirable to enlarge the wellbore below the terminal end of the previously cased wellbore. By enlarging the wellbore, a larger annular area is provided for subsequently installing and cementing a larger casing string than would have been possible otherwise. Accordingly, by enlarging the wellbore below the previously cased wellbore, the bottom of the formation can be reached with comparatively larger diameter casing, thereby providing more flow area for the production of oil and gas.
Various methods have been devised for passing a drilling assembly through a cased wellbore, or in conjunction with expandable casing to enlarge the wellbore. One such method involves the use of an underreamer, which has basically two operative states—a closed or collapsed state, where the diameter of the tool is sufficiently small to allow the tool to pass through the existing cased wellbore, and an open or partly expanded state, where one or more arms with cutters on the ends thereof extend from the body of the tool. In this latter position, the underreamer enlarges the wellbore diameter as the tool is rotated and lowered in the wellbore.
Because the underreamer may be positioned a distance uphole from a drill bit on a distal end of the drillstring, an un-reamed portion of the wellbore, often referred to in the industry as the rat hole, may exist between the underreamer and the drill bit after the borehole is enlarged. In certain instances, the distance may be up to 125 feet or more. To underream the rat hole, the first underreamer is often removed from the wellbore and replaced with a second underreamer, requiring multiple trips into the wellbore.
Accordingly, there exists a need for an integrated reamer system capable of fully underreaming a wellbore and providing measurement data of the enlarged wellbore.